Regarding a glassless 3D display method, Parallax Stereogram was proposed by F. E Ives of the United States in 1903. In Parallax Stereogram, a left image and a right image area alternately arranged at an appropriate distance on the rear surface of a parallax barrier to separate the left and right images and allow a viewer to view a stereoscopic image. More specifically, in the 3D display method using the parallax barrier, thin stripe vertical slits for transmitting or shielding light are arranged at regular intervals and left and right images are alternately disposed at the front or back of the slits by an appropriate interval, and as a result, the left and right images are geometric-optically split when the image is viewed through the slit at a predetermined point of time, thus causing the viewer to acquire the cubic effect. That is, a stripe parallax barrier optical plate serving as special glasses is installed in front of a monitor screen to allow the viewer to recognize the stereoscopic image without wearing the glasses.
However, the glassless 3D display method using the parallax barrier has a disadvantage that the viewing position is fixed. That is, the left and right images are split only when the observer is positioned at a specific distance from the screen, and hence the observer cannot view a 3D image if they move out of the viewing position. Accordingly, there was proposed a method that presents two modes using a dual layer parallax barrier in order to provide various viewing positions. The proposed method is disclosed in Korean Patent Unexamined Publication No. 10-2007-0023849, in which a barrier electrode is divided into a plurality of fine barrier electrodes, and the fine barrier electrodes are combined and driven according to positions of an observer to provide an optical viewing angle. However, this method has the disadvantage that crosstalk may be generated because part of light is transmitted through the gaps between the fine barrier electrodes, and this may result in lower 3D quality. Moreover, FPCs (Flexible Printed Circuits) become expensive, and it is difficult to perform bonding.